# DENSITY BUTTONS Click here Clicking here will move

- Slides: 15

DENSITY BUTTONS Click here: Clicking here will move you to the page. clicking Clicking here will here bring reveal will you reveal some back an information. to answer. a next this page. Clicking here on here me will allow take you you toto to hear a. SIback list multipliers some of equations, information table. Clicking on the topic. here. Clicking againwill here return take again you will back tostop your to the previous sound. previous page. TOPICS Jump to… …density and molecules (two pages). Jump to… …the density equation (two pages). Jump to… …how to measure density (three pages). Jump to… …practice questions (two pages). Jump to… …exam questions (four pages).

DENSITY Density measures how much substance has been squeezed into a particular volume. For the same mass, a substance with a smaller volume has a greater density. When a substance changes state the volume changes and, because the mass doesn’t change, the density must also change. Click the e-buttons below to see how this happens at an atomic level. Each diagram contains 16 atoms. SOLID LIQUID GAS

DENSITY EQUATION The properties of density, mass and volume come together in the density equation. This shows that the density, , is equal to the mass, m, divided by the volume, V. (We use the Greek letter rho, , as the symbol of density). Density in kilograms per cubic metre kg/m 3 m = V Mass in kilograms, kg Units 1 Volume in cubic metres, m 3 Density of water = 1000 kg/m 3 Density in grams per cubic centimetre g/cm 3 Density of air = 1. 2 kg/m 3 m = V Mass in grams, g Volume in cubic centimetre, cm 3 Density of water = 1 g/cm 3 Density of air = 0. 0012 g/cm 3 Units 2

DENSITY OF ICE and WATER Ice floats on water because ice is less dense than water. The ice molecules leave small voids in the pattern which increases the volume of ice. The water molecules are closer together which produces a smaller volume and so a larger density. E IC WATER = m V

DENSITY OF A REGULAR SOLID MEASURING MASS Depth = 4 cm MEASURING VOLUME Height = 4 cm Volume = height x width x depth = 4 cm x 4 cm Volume = 64 cm 3 400 600 Width = 4 cm 800 200 0 g 1000 Mass = 600 g CALCULATING DENSITY density = = mass volume m V 600 g = 64 cm 3 density, = 9. 4 g/cm 3

DENSITY OF AN IRREGULAR SOLID MEASURING MASS MEASURING VOLUME Volume of water = 25 cm 3 Volume of water + object = 49 cm 3 Volume of object = 49 – 25 cm 3 = 50 40 120 80 40 30 160 0 g 200 Mass = 200 g 20 10 24 cm 3 CALCULATING DENSITY density = = mass volume m V 200 g = 24 cm 3 density, = 8. 3 g/cm 3

DENSITY OF A LIQUID We use a volume of 50 cm 3 of water in this case. Volume = 50 cm 3 50 MEASURING MASS 40 Mass of measuring cylinder = 100 g 30 Mass of measuring cylinder + water = 150 g Mass of water = 150 g – 100 g = 50 g 20 CALCULATING DENSITY 10 mass volume density = 150 100 200 50 m V 50 g = 50 cm 3 = density, = 1. 0 g/cm 3 0 g 250

PRACTICE QUESTION 1 Use the density equation to identify the following materials. Density Table Solid Density g/cm 3 Marble 2. 56 Copper 8. 92 Quarts 2. 64 Gold 19. 32 Platinum 21. 4 Diamond 3. 52 You have found an old penny when digging in the garden. Its mass is 26. 8 g and volume 3 cm 3 density = mass = 26. 8 g = 8. 93 g/cm volume 3 cm 3 What is the penny made from? copper 3 You have a paperweight on your desk which measures 3 cm by 4 cm by 6 cm. Its mass is 184 g. volume = 3 cm x 4 cm x 6 cm = 72 cm 3 density = mass = 184 g = 2. 56 g/cm volume 72 cm 3 What is the material? marble 3 A lost ring, with a mass of 107 g, has turned up. After filling a measuring cylinder with 10 cm 3 of water and then adding the ring, the level rises to 15 cm 3. volume = 15 cm 3 — 10 cm 3 = 5 cm 3 density = mass = 107 g volume 5 cm 3 = 21. 4 g/cm 3 What is the ring made from? platinum

PRACTICE QUESTION 2 A pupil is experimenting with three unknown liquids and obtains the following results: Liquid A: mass = 2060 grams, volume = 2000 cm 3 Liquid B: mass = 672 grams, volume = 850 cm 3 Liquid C: mass = 990 grams, volume = 1100 cm 3 How would the 3 liquids appear as layers if added carefully together in the 5 litre beaker? Density A = mass = 2060 g = 1. 03 g/cm 3 volume 2000 cm 3 You need to calculate their densities first. Density B = mass = 672 g = 0. 79 g/cm 3 volume 850 cm 3 Density C = mass = 990 g = 0. 90 g/cm 3 volume 1100 cm 3 B C A A less dense liquid will float on a more dense liquid. Liquid B is the least dense and so floats on the other two.

EXAM QUESTION 1 Mass of oil = 102 – 74 = 28 g Mass of water = 152 – 102 = 50 g

WJEC: Physics 1 June 2016 (Found. ) Q. 6 (High) Q. 1 28 50 density = mass = 28 g volume 35 cm REMEMBER: EQUATION 50 = 0. 80 g/cm 3 3 NUMBER ANSWER UNIT

EXAM QUESTION 2 - Higher WJEC: Physics 1 Jan 2016 (Higher) Q. 6 24 turbines Volume of water from one turbine = 700 m 3 per second (in table) Max volume of water from the barrage = 700 x 24 = 16, 800 m =m V m = x V = 1000 x 16, 800 = 1. 68 x 10 REMEMBER: EQUATION REARRANGE NUMBERS 3 /s 7 kg/s ANSWER UNIT

EXAM QUESTION 2 - HIGHER Maximum power = 24 x 10 MW = 240 MW P = V x I You can use 240, 000 watt and 3, 500 volts here. I = P = 240 MW = 240 x 10 6 = 6. 86 x 10 V 3. 5 k. V 3. 5 x 10 3 4 = 68. 6 k. A 68, 600 % efficiency = useful power output x 100% total power input = 10 MW x 100% = 62. 5% 16 MW As both values are in megawatts there is no need to change them. 62. 5%

EQUATIONS r e igh h er h hig Open the file “Maths for Physics” for more about the use of mathematics in Physics.

SI MULTIPLIERS p - pico k - kilo n - nano M - mega - micro G - giga m - milli T - tera You only see the letter of the prefix on an exam paper, NOT the name. On a Foundation paper only milli, kilo and mega are used.